This invention is comprised of a pulling and pushing apparatus for installing cables, and especially fibre optic cables, in conduits between chambers. The chambers are still called pulling chambers as the traditional pulling method was used in them, especially for high-capacity metallic circuit cables.
With the development of local networks in low-capacity fibre optic cables which are very light and which have a diameter in the range of two to three millimetres, civil micro-engineering conduits were developed that are each composed of several conduits six to seven millimetres in diameter.
There are several known methods for installing cable in the conduits, among which we can cite: traditional pulling using a flexible traction line in a pulling chamber at the lower end of the conduit, the pulling of which is sometimes accompanied by additional pushing at the head of the conduit; pulling with a shuttle while using a fluid that is introduced into the chamber at the head of the conduit and which acts on the sealed shuttle attached to the lower end of the cable, this pulling with the shuttle can also be accompanied by an additional pusher at the head of the conduit; the carrying is accomplished using a fluid under pressure which circulates at high speed in the conduit starting from the head of the cable and draws the cable with it, the carrying can also be accompanied by additional pushing.
Traditional pulling and shuttle pulling are well known. Portage, of recent use, has been the subject of several descriptions, for example in documents EP-A-0 108 590, EP-A-0 292 037. Other documents, such as EP-A-0 445 622, EP-A-0 544 388, CH-A-587 575 describe methods similar to carrying.
In document EP-A-0 108 590 published on 16.05.84, there is a description of a carrying process for pulling optical fibres girdled by soft light weights in a conduit previously installed on-site. Inside the conduit the friction of the fluid flowing through it at high speed over the cable exerts a pulling force and pulls the cable along with it. The document also describes an example of making an apparatus which, placed at the head of the conduit, contains an enclosure in which a high pressure fluid source feeds the conduit in the direction of pulling the cable and, in addition, contains a pair of rubberized drive wheels aimed at compensating for the force in the opposite direction of the girdled fibres"" advance due to the prevailing positive pressure inside the enclosure at the cable""s entry point.
In document FR-A-0 292 037 published on 23.11.88, there is also a description of an apparatus which differs from the apparatus described in document EP-A-0 108 590 by the nature and function of the pushing mechanism as, in addition to the compensation for the above-mentioned opposing forces, the pushing mechanism is capable of providing an additional essential push to add to the insufficient force exerted by the carrying force, in order to allow a heavy rigid cable to be fed through it.
In document EP-A-0 445 622 published on 11.09.91 for the installation of a fibre optic cable, especially in a vertical conduit, there is a description of a pulling apparatus which reduces the friction effect, in which the flow of the fluid is created in the direction opposite to the cable""s advance, this flow causing a buoyancy which works according to Archimedes"" principle, and which moves the cable away from the conduit""s wall and reduces the mechanical friction.
In document EP-A-0 544 388 published on 02.06.93, a portable apparatus is described which is used to make a cable move along inside a conduit by applying to it a stream of liquid with a Coanda effect.
In document CH-A-587 575 on 13.03.77, there is a description of a compressed air pistol used to propel a length of thread inside a canal provided in a wall for housing electrical wires.
The traditional methods, with or without a shuttle, and the methods which use a liquid under pressure for carrying purposes or for creating buoyancy according to Archimedes"" principle, and combinations of them, have given industrialists the opportunity to propose equipment which are specific to each of the above-mentioned methods. Thus, for example, pulling requires a winch with a device to measure and regulate the traction exerted; for the push-pull with a liquid medium referred to in the documents cited above, several different devices have been proposed. Each of these different devices represents a sizeable investment which increases the cost of the controlled installation of fibre optic cables in work sites either inside or outside buildings, or between them.
One purpose of the invention described herein consists of providing a universal portable apparatus for the controlled installation of fibre optic cables in conduits in civil micro-engineering. By controlled installation, we mean the introduction of a cable into a conduit inside or outside a building by a mechanical means which exerts traction or a thrust on the cable, the traction or the thrust does not exceed a set value supplied by the operator on the basis of the values indicated by the cable manufacturer, or on the basis of the device""s calibration operation performed on the work site.
By portable, we mean a light apparatus, easily transported and used by a single operator in a tight space.
By universal, we mean a cable installation apparatus which serves as a winch or pulling capstan, intermediary carrier and puller-pusher of a liquid medium injection and carrying device, which can be driven by any type of mechanical energy source turning at a controlled speed, for example an electric or pneumatic hand drill of the type commonly used on construction sites.
We already know of such portable pushing and pulling devices for conduit cable installation and we may refer, among others, to patent documents WO-A-95 23988 and FR-A-2551 593. Generally, such a device is of the type that has, on the one hand, a drive capstan driven by a rotary drive shaft mounted in a handle and, on the other hand, an idler disk with an axle parallel to that of the capstan, and the capstan and the disk are designed to receive a cable to be driven and held between them.
For example, the capstan and the disk are housed in a casing that is formed of a base connected to the handle and a cover. A hinged joint is provided to connect the base and the cover on the short side, as well as a set of screws for ensuring the closure of the cover on the base.
We have attempted to provide an apparatus built in such a way that the thrust and pull force remains constant under all conditions of use.
In relation thereto, according to the present invention, an apparatus built according to this invention is characterized by the fact that it contains, in the handle, between the drive shaft and the power take-off, a torque regulating device at one of its ends for the torque limiting clutch which indicates the amount of the maximum pushing or pulling force selected by the operator.
According to another characteristic of the invention, it includes a means of regulating the radial pressure which the idler disk exerts on the cable to be handled. The regulation device is appropriately comprised of an angle bracket formed by two arms on the corner of which the axle of the idler disk is mounted, one of the arms is mounted on a fixed pivot perpendicular to the bottom of a hollow in the base in which is found the idler disk and the other bearing a nut through which a regulating screw pivoting around a pivot fixed in relation to the base passes, and the regulating screw which is capable of being turned at will by the operator by the use of an external thumb wheel.
According to another characteristic of the invention, in the central area of the base of the cover an inspection hole appears, which makes it possible to at least partially see the idler disk and evaluate how the cable is driving it.
According to another characteristic of the invention, the base has a compressed air inlet valve so that, when closed, the interior of the apparatus can be pressurized and the exit bushing, through which the cable to be pushed comes out, has an internal diameter which is greater than that of the cable so that the pressurized air can escape through it between the cable and the internal cylindrical wall of the exit. Moreover, the entry bushing, through which the cable to be pushed enters, is appropriately designed to be used to mount, on the inside, a sealing nipple through which the cable passes as it enters the apparatus.
The nipple also appropriately includes a circular hollow foot which fits into a circular groove in the entry bushing, extended by a hollow cylindrical body, then by a hollow conical point, the material of which forms the point which is translucid or transparent, the point is cut in such a way that the circle formed by the cut ensures a seal around the cable.
According to another characteristic of the invention, on each side of the base is found the first half couplings provided on the edges of the base and extended in an external flange, each of the half couplings respectively bear a bushing of which the external diameter corresponds to that of the first half couplings and of which the internal diameter depends on that of the cable to be driven, and, facing the first half couplings are the edges of the cover which holds the second half couplings, which, when the apparatus is closed, will fit into the first half couplings and form rotation sleeves into which the bushings are respectively housed.
According to another characteristic of the invention, the idler disk has a magnet on its outer edge that drives a revolution counter of which the display is visible in a window in the cover. According to another characteristic of the invention, the apparatus has an associated shuttle which has a cylindrical axial rod that itself has a tip in the shape of a larger hemispheric head, followed towards the back by a flared skirt which starts from the periphery and continues until it meets a fine raised ring.
According to another characteristic of the invention, on the exit side where the cable to be pushed comes out, there is an entry orifice of which the axis is tangent to the capstan, as the entry orifice is formed by cylindrical half couplings respectively provided in the edges of the base and the cover.